1. Field of the Invention
The invention relates to pre-heating hydrocarbon feedstock materials prior to cracking the feedstock. More specifically, the invention relates to the separation of the liquid and vapor components of the feedstock.
2. Description of Related Art
The concept of a flow-through cyclone, for separation of solids or liquids from a carrier gas, is well established in the literature.
Assignee""s present olefins gas oil steam cracker plant uses a separator (or knock-out pot) to separate heavy hydrocarbon in the feed before the vaporizable fraction of the heavy feed enters the radiant tubes of a pyrolysis furnace.
The vane portion of the vapor/liquid separator design disclosed herein, which is used to impart the centrifugal force necessary for separation of the incoming gas and liquid phases, is similar to that originally designed by Assignee and which is currently used in Assignee""s Catalytic Cracking Unit""s (CCU) xe2x80x9cthird-stage separatorsxe2x80x9d(TSS), for separating very fine (typically less than 20 micron) solid catalyst particles from flue gas exiting CCU regenerator vessels. This work focused on separation of dry cat cracking catalyst from a vapor stream, flow was downward through the vane assembly, then the gas would reverse and flow upward through the central hub. Catalyst fines drop out through the bottom of the separator. The vane design disclosed herein was selected since it provides a very smooth aerodynamic acceleration and spin to the incoming gas/liquid mixture necessary to achieve high separation efficiency and low pressure loss. The vane design is further distinguished by its lack of stagnant zones which would lead to areas of coke deposition. In addition, unlike conventional tangential entry type cyclone separators which typically feature a single, asymmetrical inlet slot or pipe opening, the vane itself is comprised of a series of vane elements or blades which are responsible for imparting a uniform centrifugal force to the incoming gas/liquid mixture along the entire circumference of the inlet section of the vapor/liquid separator.
A specially designed centrifugal vapor/liquid separator separates the vapor and liquid in a flash of hydrocarbon and steam mixture, such that only the vapor stream is fed and processed further downstream. The design of the separator ensures that all partially wetted surfaces in the separator, except at the vapor outlet pipe, are well wetted and washed by the non-vaporized liquid portion of the feed. The surface wetting requirement ensures that no coke deposition that would eventually lead to plugging of the separator occurs inside the separator. With the surface-wetting provision preventing coking, the flash temperature in the separator can be increased beyond the typical limit (limited because of the coking concern), thus achieving a deeper cut into the feed and enabling the recovery of a larger fraction of the feed as vapor for further downstream processing.
One application of the instant vapor/liquid separator is in pre-processing heavy olefins plant feed (crude or condensates) by flashing the hydrocarbon feed with steam at high temperature, then mechanically separating the non-vaporizable liquid fraction by this vapor/liquid separator so that only the vaporizable fraction of the feed is fed further downstream to be processed in the radiant tubes of a thermal pyrolysis furnace. The liquid, non-vaporizable portion contains heavy hydrocarbons such as pitch which are separated and sent to a coker, cat cracker, or other residue-processing units for further processing, or as fuel.
This particular invention further distinguishes itself by relying on uniformly wetted walls to mitigate coking that would reduce the service life of a normally operated, non-irrigated cyclone. The multiple-inlet type of vane design described herein is especially well suited to the creation and maintenance of a uniform film of irrigating liquid on the internal surfaces of the vapor/liquid separator.